The manuscript „Sea ice variability and links to East Siberian permafrost carbon remobilization during the last glacial-interglacial transition“ by Eriksson et al. addresses the important aspect of coastal erosion contributing organic carbon to the Arctic Ocean during time intervals of climate warming. The authors specifically investigate sea ice conditions recorded in a sediment core from the southern Lomonosov Ridge throughout the past 27 ka and how these may have impacted the stability of permafrost in the Laptev Sea region. By means of the sea ice biomarker IP25, phytplankton and terrestrial biomarkers, the authors provide a continuous record documenting periods of permanent sea ice cover during peak glacial times versus reduced sea ice cover during the Holocene and a variable organic matter export from land reaching the core site. Drawing on previously published data from the sediment core, the authors interpret this input of terrigenous organic matter in the context of coastal and permafrost erosion driven by changes in sea-ice cover and/or sea level rise. The manuscript is generally well written and the data a valuable contribution to the assessment of ice-ocean-land interactions and I hence recommend publication. However, the manuscript also exhibits some weaknesses, regarding the interpretation of own but also of previously published data. In several instances, relevant literature has not been adequately taken into account, and some published findings are represented inaccurately or interpreted in a manner that is not fully consistent with the original reports (see detailed comments below). Addressing these issues would further strengthen the manuscript and improve its scientific rigor. Regarding the interpretation if either sea ice or sea level change drove coastal erosion and organic matter export during the deglacial, it would, for example, be helpful to include a sea level record in one of the figures and to also discuss local records investigating deglacial sea level rise in the Laptev Sea (e.g. Bauch et al., 2001; Taldenkova et al., 2013). More specific comments are listed below.

Line 10: something is wrong with the wording here

Line 11: please correct here and elsewehre B.P. (not B.P)

Line 15: (Ice Proxy 25)

Line 21: delete ‘over’

Line 35: delete ‘with’

Line 39: here, you could also mention the role played by expanded sea ice in shifting the westerly winds southward (and thus reducing the impact of warm/moist air on permafrost) – see e.g. Vandenberghe et al. (2012)

Lines 40-41: Vaks et al. (2020) is maybe not the best reference regarding “past periods of abrupt climate change” as their study rather deals with the onset of perennial sea ice cover affecting moisture transport 400 kyrs ago

Line 53: (Ice Proxy with a 25 carbon atom skeleton; Belt et al., 2007)

Line 53: I suggest to rephrase: “the application of IP25 is limited by two scenarios that result in the lack of IP25: the absence of an ice cover (which serves as the habitat for the sea ice diatoms that synthesise IP25), and the presence of a permanent and thick ice cover that limits the light penetration through the ice and, consequently, the growth of sea ice diatoms (Müller et al., 2009)”.

Line 71: please specify that it is Late Pleistocene

Line 120: replace ‘content’ with ‘compounds’

Line 133: “Identification of IP25 was based on the retention times of the compound in reference sediments”. Were at least some of the samples analyzed in full scan mode (to get mass spectra)? This would be very helpful for a more reliable identification of IP25. The C25 HBI monoene and diene have a very similar retention time and often overlap, and here mass spectra would be crucial for a proper identification of IP25.

Line 136-137: have any instrumental response factors been considered for the quantification of the HBIs and sterols? If not, this is ok, but please state it as it may be relevant for quantitative comparisons with other published records.

Line 155: please add a sentence on how the fluxes were determined

Lines 196-197: “The DO-3 event (28-27.5 kyr B.P) is likely recorded in 31-PC (spanning 27.2 ± 2.3/-1.4 kyr B.P”. Looking at figure 3 and lines 155 -157, there seem to be no data points covering the DO-3 event. The first signals date to 27.2 ka - so the discussion of DO-3 is a bit misleading here. It may be helpful if you further explain the age model uncertainty for this section of the core and indicate this in the figure.

Line 198: seasonal sea ice ‘cover’ (not ‘conditions’)

Line 202: seasonal sea ice ‘cover’ (not ‘conditions’)

Line 219- 221: this sounds like a concluding remark and I suggest moving this sentence to the conclusion accordingly - and please remove one of the two ‘impacts’

Line 231: please explain HS-1

Line 233: I suggest to rephrase “...that thick sea ice inhibited the growth of open-water phytoplankton but also hindered ice algae growth by limiting light penetration through the ice”

Line 237-238: could polynyas have played a role here, too?

Lines 244 and following: this line of reasoning is a bit difficult to follow. Just a few lines earlier, you state that other records from the Laptev Sea indicate seasonal or ice-free conditions at the continental shelf during HS-1. Since these sites are located closer to the coast, the argument that a permanent ice cover (recorded at 31-PC on the southern Lomonosov Ridge) would have reduced coastal erosion does not hold up.

Lines 247-249: here, you note that permanent sea ice cover minimized the erosion/input of older carbon, whereas pre-depositional 14C ages reach their maximum between 26 and 24 ka (Fig. 5)

Line 274: I suggest to delete “in the context of sea ice”

Line 278: in addition to sea level rise, could it be that atmospheric warming has also contributed to the increased thawing of older permafrost deposits?

Line 279: looking at figure 5, MWP-1A (14.5 – 14 ka BP) actually coincides with a drop in pre-depositional 14C ages...

Line 284: same comment as above for HS-1: permanent sea ice at site 31-PC but seasonal/ice-free conditions at more coastal sites in the Laptev Sea during the B/A permitting coastal erosion

Line 296: During the PB/EH transition,

Line 300: I guess you mean “warm early (not late) Holocene” - however, Hörner et al. (2016) identify a decreasing sea ice cover during the early Holocene

Line 303 and 304: again, Hörner et al. (2016) (and Lin et al. 2024) actually report a decrease in sea ice cover during the early Holocene. The PIP25 record of core PS51/154-11 shown in figure 4 is a bit misleading here as Hörner et al. (2016) point out that additional (freshwater-derived) brassicasterol affects the interpretation of this lipid as phytoplankton marker in this time interval (which also limits its usefulness for calculating the PIP25 index). Maybe core PS51/159 discussed by Hörner et al. (2016) is better suited?

Line 309-311: looking at the pre-depositional ages of core 31-PC in figure 5, there is just one data point reflecting an old (ca. 15000 year) 14C-OC age at ca. 9 ka (while MWP-1B occured distinctly earlier at ca. 11.3 ka BP) – I suggest to rephrase this sentence

Line 321: “...phytoplankton and sea ice algae productivity”

Line 336: “...using the sea ice biomarker IP25 and open-water algae biomarkers...”

Figures

• I suggest to change the order of figures 2 and 3 as figure 2 already contains an interpretation
• Figure 5: please explain the light green shading in panel (a)

References

Bauch, H.A., Mueller-Lupp, T., Taldenkova, E., Spielhagen, R.F., Kassens, H., Grootes, P.M., Thiede, J., Heinemeier, J. and Petryashov, V.V. (2001) Chronology of the Holocene transgression at the North Siberian margin. Global and Planetary Change 31, 125-139.

Müller, J., Massé, G., Stein, R. and Belt, S.T. (2009) Variability of sea-ice conditions in the Fram Strait over the past 30,000 years. Nature Geoscience 2, 772-776.

Stein, R., Frederichs, T., Fahl, K., Geibert, W., Matthiessen, J., Niessen, F., Vogt, C., Sassenroth, C. and Bazhenova, E. (2025) A 430 kyr record of ice-sheet dynamics and organic-carbon burial in the central Eurasian Arctic Ocean. Nature Communications 16, 3822.

Taldenkova, E., Bauch, H.A., Stepanova, A., Ovsepyan, Y., Pogodina, I., Klyuvitkina, T. and Nikolaev, S. (2013) Reprint of: Benthic and planktic community changes at the North Siberian margin in response to Atlantic water mass variability since last deglacial times. Marine Micropaleontology 99, 29-44.

Vandenberghe, J., Renssen, H., Roche, D.M., Goosse, H., Velichko, A.A., Gorbunov, A. and Levavasseur, G. (2012) Eurasian permafrost instability constrained by reduced sea-ice cover. Quaternary Science Reviews 34, 16-23.

General Comments:

Eriksson et al. have produced an interesting and relevant dataset to investigate the connections between changes in sea-ice coverage on the southern Lomonosov Ridge and the input of terrestrial organic matter. The data are worthy of publications. The paper could use some polishing, some lines of evidence are not clearly laid out, and error estimates need to be produced in order to be able to fully diagnose the validity of claims made in the paper. I recommend the authors make moderate revisions to their manuscript.

In the methods section, the authors need to describe how they calculated parameters used in the paper like the limit of detection for biomarkers. Additionally, none of the figures they show contain uncertainty estimates for the biomarker concentrations/fluxes, for isotope ratios, or for derived parameters such as pre-depositional ¹⁴C ages. All of the figures must include error bars or envelopes.

Section and/or Line-specific Comments

Methods

The age model for the core in this study was made in past papers but there are no details in this manuscript for what it is – it would be good to provide some cursory background – especially when it comes to things like stitching the multicore and piston core together. Were samples in this study only analyzed on the piston core or also the multicore? Perhaps the authors could provide some details about some characteristics for the cores, like the accumulation rates – not everyone who reads this paper will refer back to the previously published papers, and it is good to provide the reader at least some mild detail here.

Is the d13C of OC really from AMS? The AMS is often significantly fractionating such that the d13C values are not accurate. Have the d13C values of OC been verified with external accuracy standards?

More details on the age model are needed to verify that equation 4 is not circular – the authors use the age model to predict the initial 14C of the samples – but are the 14C of the samples being used to calculate the age model? Does the age model derive from radiocarbon dates on, say, carbonates or other organic molecules rather than the OC dated here? Is the material being dated in this study TOC, TC, TIC, or something else? This needs to be explained more clearly and specifically in the methods section.

Fig 3 – LOD is not defined in the methods section, how is this calculated?

Results

Lines 155-160 – Be careful of phrasing. “Relatively” elevated – relative to what? “Massive” fluxes is subjective – for a results section there is some editorializing that should perhaps remain in the discussion – a description of how the values of different biomarkers change through time would suffice here.

Discussion

Lines 197-199: I am confused about the description here. It looks as if DO-3 is actually not recorded in the core, according to figure 3, but rather the time period immediately following DO-3. There are no data points in the yellow shaded area corresponding to DO-3. These lines also refer to “relatively low” PIP-25, however the PIP-25 values are nearly as high as the LGM. Don’t the values of PIP-25 in the time interval following DO-3 simply indicate seasonal sea-ice coverage?

Line 200 – the timing of LGM sea-ice onset is roughly coincident with what Pavia et al. (2025) observed using the D(Th-He) proxy at the BC28 site on the Lomonosov Ridge.

Line 205 – Why would nutrient input result from sea ice loss during this brief time period? Is it clear that this wouldn’t lead to stratification and reduced nutrient supply from below?

Section 4.2. – Again, this is consistent with the results of Pavia et al. 2025 for both the Mendeleev Ridge and the Lomonosov Ridge, inferring permanent sea ice coverage during the LGM and through HS-1.

Lines 305-306 and Lines 325-326: The authors should be very precise about what they mean here. “Orbital forcing”, implies that the authors are inferring a direct effect of increased solar radiation on the heat budget of the surface Arctic leading to sea ice melt. To prove this point, the authors could calculate whether the Early Holocene increasing in NH summer insolation is sufficient to supply the heat necessary to melt sea ice over a given area – I suspect they will find that it isn’t enough. The authors likely mean that atmospheric temperature increases, rather than ocean warming or Atlantification, are responsible for the sea ice decline – which are also consistent with the results of Pavia et al. 2025.